Omdetect creates a ds9 region file if the parameter regionfile is set equal to some file name. When the input image is viewed using ds9 the sources can be overlaid on the image by selecting the region file.
For each source, an ellipse is drawn in either green or cyan, if it is “point-like” or “extended”, respectively. The axes lengths and position angle of the ellipse are proportional to those computed for the source. The number of the source is also plotted. For each quality flag set for the source, another ellipse is also drawn, with slightly larger axes, with the corresponding colour given above for the flag.
Thus, when an image is displayed using ds9 and the regions overlayed, a point-source may be surrounded by one or more rings, each one indicating that a particular quality flag has been set. Unfortunately, due to the small number of colours that ds9 uses, some flag settings have the same colour.
In the case of source-detection on mosaiced sky-images, many of the quality-flags will not be set by omdetect (specifically bits 1, 2, 3 and 5 and bit 7 will not be set for the majority of sources). However, the colour-scheme above still applies, but the region file is less useful for seeing potential source-quality problems.
Please note that these flag values are summarized in the SRCLIST header of the source-list file.
XMM-Newton SOC -- 2021-11-30